Production of casein yarn



Patented June 27, 1950 PRODUCTION OF CASEIN YARN Robert F. Peterson, Philadelphia, Pa., assignor to the United States of America as represented by I the Secretary of Agriculture No Drawing. Application June 13, 1947,

' Serial No. 754,583

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 2 Claims.

This application is made .under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and .used by or for the Government of the United States of Americafor governmental purposes without the payment to me of any royalty thereon.

This invention relates to casein yarn, and has among its objects a process of producing yarn in a simple and expeditious manner from casein fibers having enhanced tensile strength, softness and flexibility.

It is known that casein fiber may be spun from an alkaline solution of casein into a precipitating bath of about 10% sulfuric acid and 14% sodium sulfate, and the fiber then stretched while passing through a heated hardening bath containing about 10% aluminum sulfate, 10% sodium sulfate and formaldehyde. Analyses of the fiber at this stage show that it contains only 0.2 to 0.5% combined formaldehyde not removed by washing. In order to be dimensionally stable in the unrelaxed state, the fiber must contain about 1.5% reacted formaldehyde. The time to attain this amount might require as long as 30 minutes of processin under tension. The rate of the formaldehyde reaction may be increased by raising the temperature, but this rate passes through a maximum in most baths so that higher temperatures remove formaldehyde and reverse the hardening reaction.

In order to produce dimensionally stable fiber under these conditions, it may be wound under tension onto a bobbin to prevent shrinkage and loss of tensile strength, and the bobbin and fiber placed in the formaldehyde and salt solution for the required time. In this procedure, however, enough shrinkage occurs to felt the inner layers of fiber on the bobbin together so that the bobbin can be unwound only partially, and much of the fiber is wasted.

To construct the fiber spinning machine so that the requisite formaldehyde needed to stabilize the fiber is reacted without winding the fiber requires a considerably increased floor space for each unit.

Some improvement may be obtained by substituting an acetic acid precipitating bath for the sulfuric acid bath, using 5 to acetic acid and saturated sodium sulfate solution. If, now, the fiber from this bath is wound on a bobbin and placed in the formaldehyde and salt solution in the manner mentioned above, all the finished fiber will unwind from the bobbin, but the individual fibers within the tow will be partially fused, and the yarn produced from them cannot be knit as it lacks flexibility. The only advantage attaching to the use of such acetic acid precipitating bath isthat the shrinkage of the fibers after the removal of tension will be reduced compared to fibers from the sulfuric acid bath.

In general, according to the present invention, threads of an alkaline casein solution are extruded or spun into an organic acid precipitating bath in the usual manner to precipitate the casein into fibers, and the precipitated fibers then treated under tension in a heated fixing solution containing a metal salt and'formaldehyde for a short interval to give partially hardened fibers having about from 0.2 to 0.5% combined formaldehyde. The fibers are then immediately immersed in a concentrated buffer solution havin a pH of 6 to 8. This stabilizes the fibers and further strengthen-s and hardens them so that they can immediately thereafter be spun into yarn under tension, even using the so-called pot centrifuge method, which is drastic in its tendency to unite the fibers, with out the fibers being stuck together either within the yarn by the twisting a-s they enter the funnel of the centrifuge or between the layers of yarn in the cake.

The following example exhibits the processin greater detail.

An aqueous solution. containing 20% casein and 0.4% NaOH was spun at room temperature into a precipitating bath containing 5% acetic acid, 20% sodium sulfate and 5% glucose. The spinnerette used contained 250 holes each of .003 inch diameter, the gear pump delivered 5.4 ml. of casein solution per minute, and the extruded threads traveled through the precipitating bath for 20 inches. The draW-oif wheel operated at a surface speed of 9 meters a minute, and the tow passed next to a set of conical grooved rollers spaced a meter apart, the lower of which dipped into a heated aqueous fixing solution containing 10% aluminum sulfate, 10% sodium sulfate and 5% formaldehyde, and held at C. The tow made 5 loops in passing from the inner 4-inch diameter grooves to the outer 8-inch diameter grooves, and thus was under sufiicient tension to receive a stretch. An additional 83% stretch was imposed on the tow as it left the conical rolls by running the next set of rolls at a higher speed.

On this next set of cylindrical rolls, the fiber was stabilized with the bath buffered to a pI-I of 6 by immersing the lower roller in a 30% aqueous sodium acetate solution.

The fiber was then immediately spun into yarn by being dropped into the tunnel of a centrifuge unit similar to those used in spinning viscose rayon by the pot method. The cake of yarn was removed every 2 to 3 hours, washed to remove soluble salts, and dried in a circulating air dryer.

The resulting yarn was about 400 denier, and had a tenacity of 1 gram per-"denier dry and one-half gram per denier wet. The breaking elongation was about 50% either with the fiber dry or wet. The yarn thus produced knits well on a knitting machine and the finished fabrics have a soft, silky feel, are a lustrous white, and can be dyed easily.

In the above example, other lower fattya'ci'ds or hydroxy fatty acids, such as formic acid or lactic acid, may be substituted for the acetic acid in making up the precipitating bath, and other .metal salts such as salts of chromium, zirconium .and beryllium maybe substituted for the aluminum sulfate in the heated salt bath.

It is essential, however, that the pI-I of the concentrated buffer solution be controlled to the limits indicated, and that the treatment be given immediately following the treatment in the hot saltbath (that is, prior to spinning the-fiber in the yarn), for if the fibers be spun into yarn or wound without the treatment, .they will be stucktogether in the yarn, and immersion in the buffer-solution thereafter is of no avail.

The resulting yarn is eminently suited for knitting. It is soft-and flexible, and the knitted fabrics made irorn it have the scroop characteristic of silk. This action of the concentrated .buifer 'is unexpected, since even-fibers washed at pI-I5 where hydration should be at a minimum do \not exhibit this softness. The softness is increased tenfold by washing at pH 6 instead.

stiflness of the last column was measured in each case at degrees angle of bending.

. The pH 6 wash softens the fiber until the yarn :is comparable-tea 300 denier viscose yarn which has been oiled,.ready for knitting. The casein yarns measured were not oiled. If the stifier yarns are oiled and subjected to considerable mechanical working, the yarn adhesions can be partially broken up, but the softness still does not approach that of the fiber washed at pH 6. In ad dition, many of the filaments of such stifier yarn are broken, and this provides an added source of trouble during. knitting. Also, the knitted fabrics from these yarns are harsh and stiiif.

Having thus described the invention',what is claimed is: i f

1. A process ofproducing casein 'y'arncoinprising extruding threads of an alkaline solution of casein into an organic acid precipitating bath to precipitate the casein'into fibers, treating the precipitated fibers under tension with a heated fixing solution containingja metal salt'fand formaldehyde to give partially hardenedfiber's, then immediately immersing the. partially hardened fibers in a concentrated buffer solution having a pH of 6 to 8 to 'stabilizethe fibers andfu'rther to harden and strengthen them, and then immediately spinning the fibers into yarn while maintaining them under tension. 7 2. The process of claim 1, wherein the bufie'r solution consists essentially of aqueous sodium acetate. U Q

ROBERT F. PETERSON.

REFERENCES CITED The following references are of recordin the file of thispatent:

UNITED STATES PATENTS Number Name Date 2,211,961 Meigs Augzc, 1940 2,342,994 Atwood "Feb." 29,'"'1944 2,409,475 Cline oer; 15,1946 2,429,214 Biehn et al. 001;;21, 1947 

1. A PROCESS OF PRODUCING CASEIN YARN COMPRISING EXTRUDING THREADS OF AN ALKALINE SOLUTION OF CASEIN INTO AN ORGANIC ACID PRECIPITATING BATH TO PRECIPITATE THE CASEIN INTO FIBERS, TREATING THE PRECIPITATED FIBERS UNDER TENSION WITH A HEATED FIXING SOLUTION CONTAINING A METAL SALT AND FORMALDEHYDE TO GIVE PARTIALLY HARDENED FIBERS, THEN IMMEDIATELY IMMERSING THE PARTIALLY HARDENED FIBERS IN A CONCENTRATED BUFFER SOLUTION HAVING A PH OF 6 TO 8 TO STABILIZE THE FIBERS AND FURTHER TO HARDEN AND STRENGTHEN THEM, AND THEN IMMEDIATELY SPINNING THE FIBERS INTO YARN WHILE MAINTAINING THEM UNDER TENSION. 